1. Field of the Invention
The present invention relates generally to medical ventilation tubes and, more particularly, to myringotomy ventilation tubes that can be placed in the tympanic membrane of the ear to drain fluid and alleviate a buildup or reduction of pressure in the middle ear.
2. Description of the Prior Art
The installation of tubes in the tympanic membrane, which separates the middle ear from the outer ear, is a well-known remedy for treating inflammation of the middle ear or otitis media. Typically, a myringotomy is performed to create an opening in the tympanic membrane and a vent or drain in the form of a tube is inserted into the opening to permit drainage of fluid from the middle ear to alleviate a buildup or reduction of pressure in the middle ear cavity. The tube functions to maintain the opening in the tympanic membrane for a sufficient period of time following the surgery to allow pressure to equalize between the middle and outer ears. Frequently, the condition of buildup or reduction of pressure in the middle ear cavity which the tube is intended to alleviate requires that the tube remain in place for a significant period of time ranging in duration from about six to about twenty four months.
A variety of ventilation tubes for insertion into an opening in the tympanic membrane have been introduced over the years. Prior art ventilation tubes without flanges at either end are easy to insert into the myringotomy opening but are disadvantageous in that they can be accidentally extracted from the tympanic membrane. On the other hand, ventilation tubes having flanges at one or both ends are less likely to be accidentally extracted from the tympanic membrane but are difficult to insert into and extract from the myringotomy openings, tending to enlarge the myringotomy openings such that the tendency of the tubes to fall out of the membrane increases. Attempts to fabricate prior art ventilation tubes of softer materials help alleviate problems associated with insertion and removal of the tubes through openings in the tympanic membrane but contribute to problems related to bending or buckling of the tubes during insertion while detracting from the ability of the tube to maintain an opening in the tympanic membrane.
Accordingly, it is a primary object of the present invention to overcome the disadvantages of the prior art and to improve ventilation tubes of the type used in maintaining an opening in anatomical structures such as the tympanic membrane.
It is another, more specific, object of the present invention to ease insertion of a ventilation tube into an opening in an anatomical structure while preventing inadvertent extrusion and facilitating removal.
Yet another object of the present invention is to prevent enlargement of an opening in an anatomical structure, such as the tympanic membrane, in response to insertion or removal of a medical ventilation tube through the opening.
Still another object of the present invention is to form a ventilation tube as a composite structure made of two or more materials of different durometer.
It is a further object of the present invention to maintain an opening in an anatomical structure by use of a ventilation tube having a hollow shaft made of a rigid or hard material and a flange formed at a distal end of the shaft made of a softer, more flexible material.
The present invention is generally characterized in a medical ventilation tube for placement in an anatomical structure including a hollow tubular shaft having a passage formed therethrough, the hollow tubular shaft being made of a first material having a rigidity to resist bending and maintain the passage in an open condition when the ventilation tube is placed in the anatomical structure, and a flange extending outwardly from the hollow tubular shaft, the flange being made of a second material having a rigidity less than that of the first material to permit the flange to deform in response to contact with the anatomical structure. The first material is preferably a polymer having a durometer no greater than about 100 on the Shore A hardness scale, and the second material is also preferably a polymer having a durometer less than that of the first material but greater than about 20 on the Shore A hardness scale. In a most preferred embodiment, the first material is a polymer having a durometer of about 90 to about 95 on the Shore A hardness scale and a second material is a polymer having a durometer of about 50 on the Shore A hardness scale.
Another aspect of the present invention is generally characterized in a method of making a medical ventilation tube including the steps of forming a hollow tubular shaft from a first material having a rigidity to resist bending and to maintain a passage through the shaft when the ventilation tube is placed in an anatomical structure, and molding a flange onto the hollow tubular shaft using a second material having a rigidity less than that of the first material to permit the flange to be deformed in response to contact with the anatomical structure.
Some of the advantages of the present invention are that the ventilation tube can be inserted into an opening in an anatomical structure, such as the tympanic membrane, without buckling or bending of the hollow shaft, that extrusion of the ventilation tube is prevented while maintaining a passage of substantially constant diameter through the opening, and that the ventilation tube can be formed using a wide range of materials having a variety of properties suitable for improving ease of insertion and removal, preventing extrusion and maintaining structural rigidity of the ventilation tube.
Other objects and advantages of the present invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings, wherein like parts in each of the several figures are identified by the same reference characters.